EVALUATING THE MAGNITUDE OF DIFFERENTIAL ITEM FUNCTIONING IN POLYTOMOUS ITEMS

Several recent studies have investigated the application of statistica l inference procedures to the analysis of differential item functionin g (DIF) in polytomous test items that are scored on an ordinal scale. Mantel's extension of the Mantel-Haenszel test is one of several hypot hesis-testing methods for this purpose. The development of descriptive statistics for characterizing DIF in polytomous rest items has receiv ed less attention. As a step in this direction, two possible standard error formulas for the polytomous DIF index proposed by Dorans and Sch mitt were derived. These standard errors, as well as associated hypoth esis-testing procedures, were evaluated though application to simulate d data. The standard error that performed better is based on Mantel's hypergeometric model. The alternative standard error, based on a multi nomial model, tended to yield values thar were too small.